On the web version go Settings -> Account. Under the "Content" section uncheck "show me the best tweets first". iOS app has a similar setting, and it stays synced with whatever is set there so however you disable it.
It's not like I see any more ads this way, so I don't get the point. I do get a lot of stuff that isn't ads but which I didn't subscribe to and don't care about, and it's infuriating. Twitter clearly doesn't want users like me who follow only enough stuff they can actually read. Probably someone's bonus is linked to the average number of accounts followed. It's enough to make me seriously consider not bothering with Twitter any more. I wonder what that would do to their bonus? Facebook already used the same method to successfully drive down my usage of it (and therefore my viewing of ads) by at least an order of magnitude.